New Antagonism of Hindered Amine Light Stabilizers with Acidic Compounds Including Phenolic Antioxidants (Part 2) Formation Mechanism of Active Species of Peroxide Decomposition Reaction

The effect of acidic compound on the formation of active species in homolytic hydroperoxide decomposition by hindered amine light stabilizers (HALS) was studied. The hydroperoxide decomposition activity of HALS is an important to characteristics of HALS. HALS Ammonium salt, which is a fundamental compound involved in the antagonism between HALS and acidic compounds including phenolic antioxidants, was found to be a key compound for the formation of HALS nitrosonium salt, which was identified as the active species of hydroperoxide decomposition. HALS Nitrosonium salt was not formed from active species for polymer stabilization, such as nitroxide, alkoxide, or hydroxylamine of HALS, but from HALS salt. A formation mechanism of HALS nitrosonium salt is proposed. Furthermore, molecular aggregates formed between HALS and acid compounds are discussed to be important for HALS properties.